To study the effect of vascular endothelial growth factor on the healing of nano block bone grafting in critical-sized mandibular defects.

Four critical-sized defects in each side of mandible of four Beagle dogs were built. There were two groups in our study, i.e., the VEGF/nHA/coral group acted as the experimental group, and the nHA/coral group as the control group. Pure nano-hydroxyapatite/coralline blocks and VEGF-coated blocks were implanted into the above defects in a split-mouth design. In three and eight weeks, the animals were euthanized, and the angiogenesis and bone regeneration in both groups were histologically observed by Masson′s trichrome and vWF staining technique. Newly formed calcified bone was evaluated by two fluorescents labeling technique. Neovascular density of vWF immunohistochemical stained blood vessels and the percentage of fluorescent marked calcified new bone area were statistically analyzed in two independent sample t-test in SPSS 18.0.

At three weeks in two groups, from the Masson stained images, newly formed trabecular bone was obvious with immature collagen fibers disorderly arranged and blue stained. Compared to the newly-formed bone in nHA/coral group, collagen fibers in VEGF/nHA/coral group were relatively more mature and regular arranged; Osteoblasts were surrounded by osteoid bone, which evoluted into bone cells and bone lacuna; Calcium salt deposited bone cells and bone lacuna structure were blue stained. At eight weeks in both groups, blue stained bone cells and mature bone with better aligned and wider collagen fibers were observed; Mature collagen matrix secretion was significantly increased, and some woven bone formation can be easily found. In addition, immunohistochemical analysis revealed that compared to the nHA/coral samples (105 ± 31 vessels/mm²) , the VEGF/nHA/coral samples showed an increase in the neovascular density (146 ± 33 vessels/mm²) at three weeks, with a significant difference between the two groups (P< 0.05) . At eight weeks, with the increasement of bone healing time, the quantity of new blood vessels in the two groups significantly increased. The neovascular density innHA/coral group and VEGF/nHA/coral group increased to 269 ± 67 and 341 ± 71, respectively, without significant difference (P>0.05) . Fluorescence analysis results indicated that at three weeks, the percentage of calcified new bone area was (0.79 ± 0.21) % for the nHA/coral group and (1.08 ± 0.29) % for the VEGF/nHA/coral group, with a significant difference between two groups (P<0.05) . At eight weeks, fluorescence labeled new bone in periphery and internal of scaffolds was significantly increased, and yellow tetracycline fluorescence can be easily observed in the different parts of blocks in two groups. PMBF in both groups increased to (4.25 ± 1.13) % and (5.21 ± 1.07) %, respectively, with no significant difference (P>0.05) .

The local delivery of VEGF can significantly improve neovascularization and mineralization of newly formed bone at the early stage of block bone healing in this dog implantation model.